Power Assert in Ruby(See: https://github.com/k-tsj/test-unit-power_assert)

power_assert.rb

# power_assert.rb
#
# Copyright (C) 2014 Kazuki Tsujimoto, All rights reserved.
# License: BSDL
#
#   $ ruby power_assert.rb
#      "0".class == "3".to_i.times.map {|i| i + 1 }.class
#          |            |    |     |                |
#          |            |    |     |                Array
#          |            |    |     [1, 2, 3]
#          |            |    #<Enumerator: 3:times>
#          |            3
#          String

def main
  power_assert do
    "0".class == "3".to_i.times.map {|i| i + 1 }.class
  end
end

RetValue = Struct.new(:method_id, :value, :colno)

TARGET_CALLER_DIFF = {c_return: 6, return: 7}
TARGET_CALLER_INDEX = {c_return: 2, return: 3}

def power_assert
  base_caller_lengh = caller_locations.length
  path = nil
  lineno = nil
  values = []
  trace = TracePoint.new(:return, :c_return) do |tp|
    locs = tp.binding.eval('caller_locations')
    if locs.length - base_caller_lengh == TARGET_CALLER_DIFF[tp.event]
      idx = TARGET_CALLER_INDEX[tp.event]
      path ||= locs[idx].path
      lineno ||= locs[idx].lineno
      if path == locs[idx].path and lineno == locs[idx].lineno
        values << RetValue[tp.method_id, tp.return_value, nil]
      end
    end
  end
  unless trace.enable { yield }
    raise unless path
    line = open(path).each_line.drop(lineno - 1).first
    print_assersion_message(line, values)
  end
end

def print_assersion_message(line, values)
  set_colno(line, values)
  vals = values.find_all(&:colno).sort_by(&:colno).reverse
  if vals.empty?
    return
  end
  fmt = (vals[0].colno + 1).times.map {|i| vals.find {|v| v.colno == i } ? "%<#{i}>s" : ' '  }.join + "\n"
  puts line
  printf(fmt, vals.each_with_object({}) {|v, h| h[v.colno.to_s.to_sym] = '|' })
  vals.each do |i|
    printf(fmt, vals.each_with_object({}) do |j, h|
             h[j.colno.to_s.to_sym] = [i.value.inspect, '|', ' '][i.colno <=> j.colno]
           end)
  end
end

def set_colno(line, values)
  rev_values = values.reverse
  values.each do |val|
    v = rev_values.find {|i| i.method_id == val.method_id and i.colno }
    val.colno = line.index(/\b#{Regexp.escape(val.method_id)}\b/, v ? v.colno + 1 : 0)
  end
end

main